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Old 03-19-2020, 01:57 PM   #1
forte
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Default '40 Disk/Drum brakes, no rear brake problem

Car = '40 coupe
frt. brakes = Pete n Jakes disk kit = no issues we have frt. brakes
Mst. Cylinder = Pete n Jakes dual chamber manual w/ 7/8" bore, using our orig. push rod.
WilWood proportioning valve to rear brakes.
Rear brakes = orig, new
Problem = While we bleed the rear there is no pressure of fluid. No brake. Pedal goes to floor.
With in the first 2" of pedal travel we have frt. brakes grabbing. Adj. push rod with no positive outcome.
Was sent a replacement mst. cyl. on Petes dime. No difference.
I found early forum about dual chamber for drum brakes stating the orig. rear cyl. are 1- 1 1/8 bore and the mst. cylinder in my case should have been the same. Pete's catalog states our car should have the one we got.7/8".

What say you good members who have helped me enjoy my '40 Sedan as an often driven car? Now My Dad needs help.
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Old 03-19-2020, 02:17 PM   #2
JSeery
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Default Re: '40 Disk/Drum brakes, no rear brake problem

Master cylinder size is not going to be a factor in a no pressure situation. You need to determine what that issue is. I think I would work my way back up the system to see where the pressure stoppage is. What size is the brake line?
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Old 03-19-2020, 02:23 PM   #3
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Default Re: '40 Disk/Drum brakes, no rear brake problem

First check to do is unhook one rear brake cylinder and push pedal to see if fluid is getting to the rear. If it is likely something wrong with rear brakes. Not a good idea to use a MC with a smaller diameter than original as this increases pedal movement.

IMHO most likely cause of problem is rear original lockheed brakes need to be adjusted correctly before bleeding and shoes arced to the drums otherwise you will never get a pedal. IMHO I'd junk them and buy repop lincoln bendix brakes which is what I did.

Did you bench bleed the mc before installing? You also need front/rear residual pressure valves. Link shows the components for system on my 41. Message me for phone number if you want to discuss.

I used:

aluminum remote Fill corvette style 1" Bore 4 Port Master Cyl from No Limit Engineering

proportioning/brake light switch valve

residual pressure valves

metering valve so rear brakes come on first

The remote fill MC helped in that there wasn't enough room above the MC or MC interfered with frame in the 41.

Did the same on my 36 that I sold except for the remote fill as pictured with bambalino blue sheet metal. My 36 rusty MC convinced me to go aluminum with the 41

I bled mine with a MightyVac system, works great: https://www.skf.com/mityvac/products...870/index.html

https://36fordwoodie.weebly.com/earlyv8discs.html
Attached Images
File Type: jpg mcy 1.jpg (29.1 KB, 9 views)
File Type: jpg cpp.jpg (37.2 KB, 7 views)
File Type: jpg check.jpg (69.9 KB, 24 views)
File Type: jpg mv.jpg (18.1 KB, 9 views)
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Last edited by mrtexas; 03-19-2020 at 04:14 PM.
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Old 03-19-2020, 03:16 PM   #4
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Default Re: '40 Disk/Drum brakes, no rear brake problem

My guess would be that the master cylinder is not big enough. The original cylinder is 1-1/16 not 1-1/8 as stated. but 7/8 is very small. by the time you've pushed the front pads onto the disc, there's no fluid left to push the rear brake cylinders out and get them working properly.

Try adjusting the rear brakes up until they are dragging, almost enough so you can't turn the wheel. Then see if you can bleed it enough so you can feel the brake going tight.

I'd be looking for at least a 1" cylinder.

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Old 03-19-2020, 03:34 PM   #5
Als48
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Default Re: '40 Disk/Drum brakes, no rear brake problem

Have your rear cylinders been serviced/rebuilt? Any leak would cause the problem you are having with bleeding.
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Old 03-19-2020, 04:07 PM   #6
Gary Tosel
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Default Re: '40 Disk/Drum brakes, no rear brake problem

I would ask how you are bleeding the brakes? I have found that with dual chamber master cylinder, you need to pressure bleed at the master cylinder or vacuum bleed at each wheel cylinder. Using the normal brake pedal would allow the front brakes to stop with no residual to force fluid to the rear. Disc brakes do not need much fluid volume, while drum brakes need more volume.


I ended up using a hand vacuum pump and it took a long time to bleed them completely, but it worked fine. I will leave the check valve, residual valve and proportioning valve to the experts. I did use residual valves front and rear, but no proportioning valve.
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Old 03-19-2020, 05:32 PM   #7
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Default Re: '40 Disk/Drum brakes, no rear brake problem

I’m using a 7/8 disc/drum master from a Maverick. Wilwood adjustable proportioning valve. I did have to extend my pushrod about 1/4 to get full stroke. Are you sure you are getting full stroke on your master? Which chamber goes to your rear brakes? If it is the front I bet that is your issue. I can lock up all 4 tires with my setup.

All that being said I picked up a set of f1 front brakes and plan to rip this disc brake crap back out.
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Old 03-19-2020, 06:00 PM   #8
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Default Re: '40 Disk/Drum brakes, no rear brake problem

Did you bench bleed your MC before installation? This is mandatory on dual cylinders.
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Old 03-19-2020, 08:06 PM   #9
forte
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Default Re: '40 Disk/Drum brakes, no rear brake problem

Rear cyl. are new.
Yes to bench bleeding mc.
Rear chamber going to rear brakes.
But this vacuum bleeding is new to us, as is the mc pressure bleeding.
using 1/4" brake lines.
Talked to Jason @ Pete n Jakes. The way he explained the 7/8" bore, its needed because of the front disk piston. If it was larger than 7/8" there would be less pressure to work with. Or something like that. it made sense as we talked, its also what Dad reads in articles in many magazines. If people use a larger bore they don't have enough pressure. We will try the bleeding methods above.
Thank you. Will RSVP.
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Old 03-19-2020, 10:12 PM   #10
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Default Re: '40 Disk/Drum brakes, no rear brake problem

Quote:
Originally Posted by forte View Post
Rear cyl. are new.
Yes to bench bleeding mc.
Rear chamber going to rear brakes.
But this vacuum bleeding is new to us, as is the mc pressure bleeding.
using 1/4" brake lines.
Talked to Jason @ Pete n Jakes. The way he explained the 7/8" bore, its needed because of the front disk piston. If it was larger than 7/8" there would be less pressure to work with. Or something like that. it made sense as we talked, its also what Dad reads in articles in many magazines. If people use a larger bore they don't have enough pressure. We will try the bleeding methods above.
Thank you. Will RSVP.
Most important to insure rear lockheed brakes are adjusted right and the shoes make contact over the whole surface by being ground to fit. Until you have that all bets are off.
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Old 03-20-2020, 02:46 PM   #11
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Default Re: '40 Disk/Drum brakes, no rear brake problem

If you had to use an adapter for the MC mount, you need to lengthen the push rod by the amount of the adapter thickness, otherwise you will not get enough travel.. I put a BOSS 429 MC (15/16" bore), Wilwood adjustable proportion valve, on my '40 coupe over 25 years ago, and extended the push rod. Also used a manual vacuum bleeder. Brakes have been perfect since then.
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Old 03-20-2020, 04:30 PM   #12
Aarongriffey
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Default Re: '40 Disk/Drum brakes, no rear brake problem

In my 64 years of being a full time mechanic I don’t ever remember of bench bleeding..
Make sure the push rod is loose enough so it allows the master cylinder piston to move back far enough to clear the hole so brake fluid can drop down into the master cylinder bore.
I wish I lived close enough to give a hand with this problem.
With the pedal relaxed the push rod must be loose.
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Old 03-21-2020, 10:45 AM   #13
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Default Re: '40 Disk/Drum brakes, no rear brake problem

When you add the adapter to the original pedal assembly you need a longer push rod.
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Old 03-21-2020, 12:14 PM   #14
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Default Re: '40 Disk/Drum brakes, no rear brake problem

I've only done this a few times, but the Pinto/mustang system has wlways worked fine for me. However, without Power brake booster, you have to use a different set of pads in the front. I forget the color to use, give them a call.
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Old 03-21-2020, 12:21 PM   #15
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Default Re: '40 Disk/Drum brakes, no rear brake problem

I think you have a bleeding issue. Put some speed bleaders in the front and put tubes down into a can on each front wheel and crack them open so fluid can come through. Now bleed the back brakes as normal. Because the fronts are closer to the MC, once they have pressure no more or very little fluid will go toward the back. Or you could put speed bleeders on all 4 corners but the key is you have to have the fronts letting fluid out until you get the rears done. I have seen this before.
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Old 04-24-2020, 09:08 AM   #16
forte
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Default Re: '40 Disk/Drum brakes, no rear brake problem

Got a call from Dad last night. He has a brake pedal now. He will wait for me to fully bleed brakes but for what he was able to do he finally has some pressure on the pedal. From what I can understand he installed a larger mc with two equal sized cylinders and a residual valves to both front and rear brakes.
He tried a billet inside the prior mc , he was about to try a new brake pedal. I'm proud of my Dad for not giving up, doing it alone like most things he does. When the Govt. allows me to visit I will update you on more exact way of accomplishment. Thank you all for your ideas.
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Old 04-30-2020, 09:02 PM   #17
SETHDOUG
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Default Re: '40 Disk/Drum brakes, no rear brake problem

Quote:
Originally Posted by forte View Post
car = '40 coupe
frt. Brakes = pete n jakes disk kit = no issues we have frt. Brakes
mst. Cylinder = pete n jakes dual chamber manual w/ 7/8" bore, using our orig. Push rod.
Wilwood proportioning valve to rear brakes.
Rear brakes = orig, new
problem = while we bleed the rear there is no pressure of fluid. No brake. Pedal goes to floor.
With in the first 2" of pedal travel we have frt. Brakes grabbing. Adj. Push rod with no positive outcome.
Was sent a replacement mst. Cyl. On petes dime. No difference.
I found early forum about dual chamber for drum brakes stating the orig. Rear cyl. Are 1- 1 1/8 bore and the mst. Cylinder in my case should have been the same. Pete's catalog states our car should have the one we got.7/8".

What say you good members who have helped me enjoy my '40 sedan as an often driven car? Now my dad needs help.
hello mr forte ,, i have a 1935 ford cabriolet and had the very same problem
four wheel disc set up and great fronts no back pedal . I was told the backs needed to be adjusted and you will find when you remove the rear calipers that the inboard pad is not even touching the rotor about 1/=.2 inch away ,, read in your instructions how to adjust the rear caliper . Its because the set up for the e-brake is why your adjusting that inboard pad back into the rotor
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Old 04-30-2020, 11:19 PM   #18
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Default Re: '40 Disk/Drum brakes, no rear brake problem

I had a similar problem on a recent build. I used the normal Corvette 1 inch master cylinder but had little or no rear brake pressure. I went through the NAPA book and matched the rear wheel cylinders and master, from a Maverick as Jax previously stated. I think it was a 7/8 or 13/16 master. I got the brakes bled with the new setup. With the 1 in Corvette master on another build a while back it took way too much pedal effort to stop the car. I swapped that master cylinder out to the smaller diameter master and it will stop on a dime now. Everything need to be matched, master cylinder, wheel cyl's and take the weight of the car into account also.
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Old 05-01-2020, 09:21 AM   #19
41ford1
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Default Re: '40 Disk/Drum brakes, no rear brake problem

To add another version of this front disk / stock rear brake setup i used the following:
'70s GMC 3/4 ton master cylinder (1 1/8" bore) with an adapter to keep it under the floor.
Speedway disk brake kit (the one that retains 5 on 5 1/2 wheel bolt circle)
2 PSI residual valve for the front disks.
10 PSI residual valve for the rear drums.
No proportioning valve.
The adjustment of the rear is somewhat critical, They cannot be setup too loose.
Bleeding was done with a homemade pressure bleeder. A vacuum bleeder did not work for me on this system.
This system is now 9 years old. I have had no issues with this setup.
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